1. Field of the Invention
The present invention relates to a sample and hold (S/H) circuit, and more particularly, to a multi-stage S/H circuit for reducing sampling saturation.
2. Description of the Prior Art
A sample and hold circuit for a traditional touch panel may be saturated due to large instantaneous noise. The instantaneous noise may come from a power supply, a conductive substance touching the panel, a human body approaching the panel or the like, causing a difference between a sensing value of a sensor in the touch panel and a value sampled and held by the S/H circuit. In other words, the S/H circuit must discard the value sampled and held this time, and then perform S/H operation on the sensing value of the sensor in the touch panel again. As such, not only the operation time for the S/H circuit is increased, and it may not be possible to measure the original sensing value of the sensor in the touch panel in the next S/H operation. (For example, assuming in the previous S/H operation the S/H circuit has obtained 40% of the sensing value of the sensor in the touch panel, but this value is discarded due to saturation caused by the instantaneous noise, then the S/H circuit may only obtain the remaining 60% of the sensing value of the sensor in the current S/H operation).
In view of these shortcomings, the present invention thus provides a multi-stage S/H circuit that alleviates the saturation issue caused by the instantaneous noise in traditional S/H circuits.